1. Technical Field
The present invention relates generally to integrated circuits and specifically to designing integrated circuits. Still more specifically, the present invention relates to an improved method of modifying existing integrated circuit designs.
2. Description of the Related Art
Over the last few decades, the electronics industry has faced rapid growth due to the increased demand for high performance computing, telecommunications, and consumer electronics. This increase in demand primarily stems from information services that provide high bandwidth media, such as streaming audio and video.
To meet these increased demands, each generation of integrated circuits faces a shorter design cycle. Frequently, it is more economical to redesign an existing integrated circuit design to meet the requirements of a product or service.
However, modifying integrated circuit designs presents designers with a new problem. During a redesign, integrated circuit designers frequently add new circuit elements and interconnects, which may crowd the existing design. This crowding of circuit elements and interconnects introduces crosstalk noise problems into the integrated circuit design.
Crosstalk noise is typically caused by capacitive coupling of neighboring wires. For example, two signals A (aggressor) and V (victim) are driven within two neighboring wires that are each driven by respective drivers. When signal A transitions, capacitive coupling induces noise into signal V. If signal V is a steady state signal, the noise takes the form of a spike in the signal and is smoothed out by V's driver circuit after some delay. However, if signal V transitions at the same time as A's transition, the induced crosstalk noise leads to a shorter or longer transition delay, depending on the configuration of the coupled wires. Therefore, increased crosstalk noise contributes to timing failures due to the changes to the transition delay. Several factors contribute to crosstalk, such as: the shape of wires, the distance between the wires, the number of metal layers in the integrated circuit design, and the impedance of the wires that contain signals A and V.
Once new circuit elements or interconnects are introduced into the design, the specific causes of crosstalk noise may be difficult to identify. Therefore, there is a need for a method of identifying problem areas within an integrated circuit design that are susceptible to crosstalk noise.